So, I seem to be stuck in a war with no way to get out besides surrender, even though I've had the upper hand the whole time.  Basically, a neighbor with one grievance (and demand to take a territory) declared war on me long ago.  But, I was far stronger, so she never attacked.  Now, her war support has been stuck on zero for a long time.  But, since I have no grievances, I can't demand surrender or offer "white peace."  Obviously, there's no reason I should have to give up my territory for no reason.  Is this working as intended?

Ha, literally the next turn they surrendered.  *shrug*  Still, there needs to be some other way to modify potential demands after a war starts.

Agreed, there should be a way to drop or add grievances after starting a war. Perhaps paying an influence cost to represent modifying the "terms" of the war.

I've had exactly the same problem, I had a war last roughly 70 turns after an AI declared on me for refusing to hand over territory, but I just held my position, I won 5 or 6 battles, but they just kept coming back with two full stacks of 4 (It was early game). With no way of offering peace other than surrendering my land, I just had to stay in this perpetual war. 

Maybe a way to help end these wars earlier (Other than being able to offer a white peace) would be to give a war support penalty if they haven't taken the city/outpost that's the target of the war? Maybe with a grace period of a few turns.